gulpfile - shutdown mocha after test run

see:
- http://mochajs.org/#usage
- https://boneskull.com/mocha-v4-nears-release/#mochawontforceexit

gulpfile.ts

@@ -93,6 +93,7 @@ gulp.src('./src/**/*.ts')
 gulp.task('mocha', () =>
 	gulp.src([])
 		.pipe(mocha({
+			exit: true
 			//compilers: 'ts:ts-node/register'
 		} as any))
 );